Hakuba Keijiro doesn't have any interest in girls, until he meets a beautiful girl that is also very unusual. The girl in question is dressed in an old-fashioned style, and seems to have nearly complete amnesia. The only thing she remembers is that her name is "Hiiragi." Keijiro gets his parents to take guardianship of her while they look for her real family, and Hiiragi moves in. But who is she, really? Is she a princess, come through some kind of time-slip? Is she something supernatural? Hiiragi herself would like to know...